Needle thread snub



FeB. 24, 1970 5. J. KETTERER NEEDLE THREAD snus Filed Nov. s, 1958 Crank Angle (deg.)

r .e o R 3 m N8 0 wk H mu y m 4 S w 4 S O M .m N. F 0 m L ZTL w I w W m. w w 2\ p w L W/ TNESS 3,496,895 NEEDLE THREAD SNUB Stanley J. Ketterer, Morris Plains, N.J., assignor to The Singer Company, New York, N.Y., a corporation of New Jersey Filed Nov. 5, 1968, Ser. No. 773,507 Int. Cl. Db 47/04 US. Cl. 112255 5 Claims ABSTRACT OF THE DISCLOSURE A needle thread snub for a sewing machine is disclosed which comprises a thread engaging roller held captive in a tapered constraining space on the needle clamp. Because of the inertia of the roller and the effect of the direction of movement of the thread, this needle thread snub will be effective to control the size of the needle loop presented to the loop taker but will be automatically ineffective during stitch setting.

BACKGROUND OF THE INVENTION It has long been known to arrange a needle thread snubbing device between a sewing machine needle and a needle thread take-up for providing control of the size of needle thread loop presented to the loop taker. Such prior known needle thread snubbing devices, however, have had the drawback that they snub the needle thread not only during loop presentation, but as much or more at other phases of stitch formation such, as for instance, stitch setting. Because such known needle thread snubbing devices are effective at stitch setting, the needle thread tensioning devices are required to be set at correspondingly higher values thus increasing the possibility of thread breakage.

It is an object of this invention to provide a needle thread snubbing device which operates automatically to vary the snubbing action on the needle thread during the stitch forming process so as to apply a snubbing action during loop presentation and so as to remove or greatly reduce the snubbing action during stitch setting.

It is an object of this invention to provide a needle thread snubbing device of the above. character which does not require the use of any actuated parts but instead utilizes the movement of the needle thread and the inertia incident to reciprocation of a stitch forming instrumentality, such as the sewing machine needle bar, to effect auto matic variation in the snubbing action.

The above and additional objects and advantages of this invention are attained by the provision of a thread engaging roller loosely constrained on the needle clamp of a sewing machine by a bracket providing a downwardly inclined seat for the roller. Both the direction of movement of the thread, and the inertia of the roller will have influence upon the degree to which the roller snubs the thread. At the time of needle loop presentation both of the above fact-or will be favorable for thread snubbing action, i.e., the needle thread will be moving downwardly, and deceleration of the needle bar in its downward movement or acceleration upwardly will give rise to inertia forces urging the roller downwardly into the inclined seat and against the thread. At stitch setting both of the above factors will be operative to remove the snubbing action from the thread.

The invention will be described hereinbelow with 3,496,895 Patented Feb. 24, 1970 reference to a preferred embodiment illustrated in the accompanying drawing in which:

FIG. 1 represents a front elevational view of a portion of a sewing machine having the needle thread snubbing device of this invention applied thereto,

FIG. 2 is an enlarged exploded perspective view of the needle bar clamp and the needle thread snubbing device of the sewing machine of FIG. 1,

FIG. 3 is an enlarged cross-sectional view of the needle thread snubbing device taken substantially along line 33 of FIG. 1, and

FIG. 4 is a graph showing in superposition a plot of the endwise. position of needle reciprocation together with a plot of the thread which is made available by the take-up device of the sewing machine of FIG. 1.

Referring to the drawing, FIG. 1 illustrates a portion of a sewing machine including a work supporting bed 11 and a bracket arm 12 overhanging the bed. As illustrated, an endwise reciprocable needle. bar 13 is carried in the bracket arm and is operated by means of a crank 14 from a rotating shaft 15 in the bracket arm. Also actuated by the crank 14 is a needle thread take-up lever 16. As shown in FIG. 1 and in the upper portion of FIG. 2, the needle bar 13 carries at its lower extremity a needle clamp 17 which includes a block 18 within which a needle butt accommodating recess (not shown) is provided. A thumb screw 19 serves to secure the butt of a thread carrying needle 20 in the needle clamp. The needle clamp is formed with a collar 21 by which it may be fastened to the needle bar.

As is conventional in sewing machines, the needle bar carrying the needle provides one of the stitch forming instrumentalities by which threads are concatenated to form stitches. The sewing machine illustrated in FIG. 1 is of the lockstitch variety, however, the thread snubbing devices of this invention may have utility as well in chainstitch sewing machines. In FIG. 1 the needle thread indicated at T is directed from a source of supply (not shown) to a pretension device 25, then to a main tension device 26, to a check spring 27 then to the take-up lever 16. From the take-up lever the thread extends through a plain thread guide 28, then to the thread snubbing device of this invention, indicated generally at 29, and finally to the thread carrying needle 20.

In the operation of the sewing machine illustrated in FIG. 1, it is the function of the thread carrying needle to carry loops of needle thread through a work fabric and to present such loops to stitch forming instrumentalities (not shown) in the bed for concatenation into stitches. The take-up lever 16 serves to pay out a slack thread to accommodate reciprocation of the needle and manipualtion of the needle thread engaged by the stitch forming instrumentalities beneath the bed, then to draw up the slack thread into a stitch in the work fabric. The purpose of the thread snubbing device 29 of this invention is to control the downward flow of slackened thread T to the needle during this stitch forming process so that, for instance, excess slack thread does not pile up under the needle before the needle penetrates the work, and further, so that an excess of thread will not occur prior to seizure and manipulation of the thread by the stitch forming instrumentalities in the bed as the needle begins to rise. At other phases of needle reciprocation the influence of the thread snubbing device 29 does not serve a useful purpose, and in fact frictional resistance applied to the thread T by the thread snubbing device 29, for instance at the top of the needle reciprocation when the stitch is being set, may be detrimental for the reason that it would necessitate a compensating adjustment of the main tension device 26 to a higher value having in mind that the stitch must be set against the tension of the main tension device. Prior knOWn thread snubbing devices which have operated to apply a substantially constant frictional resistance to the passage of thread have thus been unsatisfactory because such frictional resistance must also be overcome at stitch setting by an added increment of tension applied by the tension device 26. Prior art thread snubbing devices of the capstan type have been known which apply a varying frictional resistance to the thread which increases as the tension on the thread increases. Capstan type thread snubbing devices may have the added disadvantage, therefore, of applying a greater frictional resistance to the thread at stitch setting than during descent and penetration of the needle.

It is a feature of the thread snubbing device of this invention that it will automatically apply a snubbing action to the needle thread T during the descent of the needle and while the needle thread T is being slackened by the take-up lever 16, and the frictional effect of the snubbing device will automatically be removed during the up stroke of the needle and during stitch setting.

As illustrated in FIGS, 2 and 3 the thread snubbing device of this invention comprises a bracket having a first limb 41 formed with curved cars 42 which embrace the collar 21 of the needle clamp, and also formed with an aperture 43 for a fastening screw 44 by which the bracket is secured to the needle clamp. The bracket 40 includes a second limb 45 which when the bracket is attached to the needle clamp is disposed in substantially parallel relation to a slabbed thread engaging surface 46. The second limb 45 is formed with a tab 47 which is struck out at an acute angle, as best illustrated in FIG. 3. The aperture 48 resulting from the struck out tab 47 together with the sloped abutment 49 provided by the inner surface of the tab 47 together define a constraining cage for a thread controlling element 50 which preferably takes the form of a cylindrical roller. The constraining cage loosely holds the thread controlling element with capacity for movement relatively to the needle clamp. When the thread controlling element is moved upwardly relative to the needle clamp, as by the influence of the thread T moving upwardly or under the influence of inertia when the needle bar is accelerating downwardly or decelerating upwardly, the thread will not be frictioned by the action of the thread controlling element 50 pressing the thread against the thread engaging surface. Conversely, when the thread controlling element 50 is moved downwardly relative to the needle bar the sloped abutment 49 will urge the thread controlling element 50 toward the slabbed thread engaging surface 46 to apply frictional resistance to a thread therebetween. The thread controlling element will move downwardly relative to the needle bar when the thread T moves downwardly or because of the inertia of the thread controlling element 50 when the needle bar is accelerating upwardly or decelerating downwardly.

In order to direct the thread leading to the needle 20 between the thread engaging surface 46 and the thread controlling element 50, the second limb 45 of the bracket 40 is formed above the tab 47 with a pair of inturned fingers 51 which are accommodated loosely in a recess 52 formed in the collar 21 of the needle clamp. With slight lateral pressure the thread may be directed between the fingers 51 to be trapped therebetween so as to guide the thread T to the action of the thread controlling element 50.

In the diagram illustrated in FIG. 4 the curve shown as a solid line indicates the needle reciprocation throughout the various crank angles of the crank 14, the crank angle marked Zero degrees corresponds to the bottom dead center of a needle reciprocation. In the curve showing needle reciprocation, the heavy line indicates that portion throughout which the inertia forces acting upon the thread controlling element 50 will urge the thread controlling element downwardly into a position for applying frictional resistance to the thread, and the portion illustrated in light lines is that in which the inertia will carry the thread controlling element 50 upwardly and out of effective contact with the thread, Shown in dot and dash lines in FIG. 4 is a thread curve indicating the thread which is made available by the operation of the stitch forming instrumentalities during stitch formation. In such a thread curve a slope downwardly to the right is indicative of slackening in the thread by the take up lever 16, and a slope of the curve upwardly to the right is indicative of the drawing action of the take up lever 16 on the thread. That portion of the thread curve in FIG. 4 which is shown in heavy lines is, therefore, indicative of movement of the thread downwardly toward the needle through the thread snubbing device 29 while that portion of the curve shown in light lines corresponds to that portion in which the thread will be moving upwardly through the thread snubbing device 29. Indicated in FIG. 4 are points of loop seizure and of stitch setting for a typical cycle of stitch formation and it will be noted that during loop seizure the combined effect of the inertia and of the downward direction of thread travel will influence the thread controlling element 50 into effective thread frictioning position; while during stitch setting, the combined effect of inertia and of the direction of thread travel through the thread snubbing device will be acting to influence the thread controlling element 50 out of engagement with the thread.

Having set forth the nature of this invention what is claimed herein is:

1. A thread snubbing device for a sewing machine having stitch forming instrumentalities and including an instrumentality reciprocable in timed relation with operation of said stitch forming instrumentalities, said thread snubbing device comprising means carried on said reciprocable instrumentality and defining opposed thread engaging surfaces, thread guiding means for directing a thread between said opposed thread engaging surfaces, one of said thread engaging surfaces being a thread contacting element shiftably supported relatively to said reciprocable instrumentality, constraining means for said thread contacting element carried on said reciprocable instrumentality, said constraining means including a. sloped abutment for urging said thread contacting element toward said opposed thread engaging surface upon shift of said thread contacting element toward one direlction of reciprocation of said reciprocable instrumenta ity.

2. A thread snubbing device as set forth in claim 1 in which said reciprocable instrumentality comprises a needle bar with a needle clamp at one end accommodating a thread carrying needle, in which one of said opposed thread engaging surfaces is fixed on said needle clamp, and in which said sloped abutment of said thread contacting element constraining means is inclined toward said fixed thread engaging surface in the direction of a thread carrying needle accommodated in said needle clamp.

3. A thread snubbing device as set forth in claim 2 in .which said thread engaging surface comprises a planar surface and in which said thread contacting element comprises a straight cylindrical roller.

4. A thread snubbing device as set forth in claim 2 in which said thread engaging surface is formed exteriorly on said needle clamp, and in which a bracket secured to said needle clamp includes both said constraining means for said thread contacting element and said means for guiding a thread between said thread contacting element and said thread engaging surface.

5. A thread snubbing device as set forth in claim 4 in which said bracket includes a first limb and a second limb, means on said first limb for attaching said bracket to said needle clamp with said second limb extending substantially parallel to said thread engaging surface, a tab struck out from said second limb at an acute angle thereto defining said constraining means including said sloped abutment for said thread contacting element, said second limb of said bracket being formed adjacent to said tab with a pair of inturned fingers, and said needle clamp being formed with a recess loosely accommodating said 10 inturned fingers to define said thread guiding means.

References Cited UNITED STATES PATENTS Willcox 112-255 XR Dugan 112-255 Murphy 112-255 Corey 112255 Patrick 112-242 MERVIN STEIN, Primary Examiner G. H. KRIZMANICH, Assistant Examiner 

